151.3.2 Greenhouse Gas Concentrations
Key indicators of global climate change also include the changing concentrations of the radiatively important GHGs that are significant drivers for this change (e.g., Denman et al., 2007;Denman, K. L., et al., 2007: Couplings between changes in the climate system and biogeochemistry. In: Climate Change 2007: [ The Physical Science Basis]. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change S., D. Qin, M. Manning, Z. Chen, M. Marquis, K. B. Averyt, M. Tignor and H. L. Miller (eds.). Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 501–587. Forster et al., 2007).Forster, P., et al., 2007: Changes in atmospheric constituents and in radiative forcing. In: Climate Change 2007: [ The Physical Science Basis]. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change S., D. Qin, M. Manning, Z. Chen, M. Marquis, K. B. Averyt, M. Tignor and H. L. Miller (eds.). Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 131–234. Figures 1.5 through 1.7 show the recent globally and annually averaged observed concentrations for the gases of most concern, CO₂, CH4, and N₂O (see Sections 2.2, 6.3 and 8.3 for more detailed discussion of these and other key gases). As discussed in the later chapters, accurate measurements of these long-lived gases come from a number of monitoring stations throughout the world. The observations in these figures are compared with the projections from the previous IPCC assessments. The model simulations begin with historical emissions up to 1990. The further evolution of these gases was described by scenario projections. TAR and AR4 model concentrations after 1990 are based on the SRES scenarios but those model results may also account for historical emissions analyses. The recent observed trends in CO₂ concentrations tend to be in the middle of the scenarios used for the projections (Figure 1.5). As discussed in Dlugokencky et al. (2009),Dlugokencky, E. J., et al., 2009: Observational constraints on recent increases in the atmospheric CH4 burden. Geophys. Res. Lett., 36, L18803. trends in CH4 showed a stabilization from 1999 to 2006, but CH4 concentrations have been increasing again starting in 2007 (see Sections 2.2 and 6.3 for more discussion on the budget and changing concentration trends for CH4). Because at the time the scenarios were developed (e.g., the SRES scenarios were developed in 2000), it was thought that past trends would continue, the scenarios used and the resulting model projections assumed in FAR through AR4 all show larger increases than those observed (Figure 1.6). Concentrations of N₂O have continued to increase at a nearly constant rate (Elkins and Dutton, 2010)Elkins, J., and G. Dutton, 2010: Nitrous oxide and sulfur hexaflouride. Section in State of the Climate in 2009. Bull. Am. Meteorol. Soc., 91, 44–45. since about 1970 as shown in Figure 1.7. The observed trends tend to be in the lower part of the projections for the previous assessments. Notes Navigation ES 1.1 1.2.1 1.2.2 1.2.3 1.3 1.3.1 1.3.2 1.3.3 1.3.4 1.3.4.1 1.3.4.2 1.3.4.3 1.4.1 1.4.2 1.4.3 1.4.4 1.5 1.5.1 1.5.2 1.6 Box 1 FAQ Refs